Information storage technology and the storage capacity available therefrom has been historically limited by a number of factors. A typical prior art Winchester magnetic storage system includes a magnetic head that has a slider element and a magnetic read/write element and is coupled to a rotary actuator magnet and coil assembly by a suspension actuator arm so as to be positioned over the surface of a spinning magnetic disc. In operation, lift forces are generated by aerodynamic interaction between the magnetic head and the spinning magnetic disc. The lift forces are opposed by spring forces applied by the suspension so that a predetermined flying height is hopefully maintained over a full radial stroke of the radial actuator assembly above the surface of the spinning magnetic disc. Such conventional magnetic heads are constrained by the theoretical limit on the ability to closely pack adjacent magnetic bits on the disc surface and still accurately recover and read each bit of information.
To address this problem, much research is being done in the development of magneto-optical (MO) storage technology which provides a higher areal density. During conventional writing of information in MO disc drives, an incident laser beam heats a selected spot of interest on the MO disc to approximately the Curie point. A time varying vertical bias magnetic field is used to define a pattern of "up" or "down" magnetic domains in a recording layer. Subsequently, as the selected spot of interest cools, information is recorded on the MO disc. The size of the magnetic field that is generated provides a lower limit on a maximum data density that may be recorded on the MO disc. Information access in the MO storage system in turn is limited by the size of the optical spot to which an incident laser beam may be focused on the disc surface. Magneto-optical information access requires the use of polarized laser light for reading and writing information on an MO disc. To read information, MO technology makes use of a magneto-optical effect (Kerr effect). To detect a modulation of polarization rotation imposed on the linearly polarized incident laser beam by the recorded domain marks in the recording layer. The polarization rotation (representing the information stored at recorded marks or in the edges of the recorded marks) is embodied in a reflection of the linearly polarized laser beam and is converted by optics and electronics for readout.
It is apparent that an important factor in the ability to accurately read and write information from an MO disc, as well as to rapidly access different storage tracks on the MO disc is the design of the flying head, which carries the various components required for accessing magneto-optical information. The need to carry an optical assembly and a magnetic coil on the flying head has made its physical size and mass rather bulky. Therefore, it is somewhat difficult to provide a head which flies at a constant height over the surface of the plastic disc that typically has large runout/waviness. This is because the slider, which is the primary part of the flying head which controls the flying characteristics, typically includes a pair of side rails which are positioned along its side edges and are disposed about a recessed area. These side rails form a pair of air bearing surfaces. As the disc rotates, the disc drags air under the slider and along the air bearing surfaces in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the side rails, the compression by the air bearing surfaces causes air pressure between the disc and the air bearing surfaces to increase, which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. The changing surface curvature associated with the runout surface will exert a varying hydrodynamic lifting force to the slider, modulating its fly height. In general, the longer rails will result in larger fly height modulation.
A related problem in establishing the glide height of a plastic disc which is especially unique to a magneto-optical disc drive is that a rotating plastic disc intrinsically exhibits larger runout/vibration than aluminum discs as long established in magnetic disc drives; this runout or vibration modulates the flight characteristics of the glide testing slider, making it difficult to reliably establish the true glide height of a plastic disc. Further, the excessive fly height fluctuation will frequently result in head disc contact and movement of the head out of optical focus. Finally, the fly head modulation introduces very unacceptable variations in the glide testing results. All of these difficulties occur with the typical catamaran ABS such as shown in FIG. 1 having twin rails 10, 12 which, it has been determined, is not the optimal design for achieving smooth disc runout/vibration following performance. Thus, a slider design which is relatively insensitive to fly height modulation characteristics to disc runout/vibration is highly desirable.